Aqua watched the creature from afar, frowning. She wasn’t sure what to make of it. She’d encountered a lot of creatures in her time in the Realm of Darkness, and the closest thing she’d seen to this thing were the small Cloudy Sunrises that she’d found (and borne the children of) a short while back.

But the creature in front of her was only superficially similar to the Cloudy Sunrises. Both of them seemed quite small, about the size of a jack-o-lantern; they were both creatures of gas or vapor and lacked the crossed-heart emblem that was so typical on many other breeds of Heartless. Yet the Cloudy Sunrise had been a creature of pale white clouds with a miniature sun overhead, the very aspect which had prompted Aqua to give the species its name. This being, on the other hand, was more typical compared to other Heartless. Its body was primarily black and purple, with dark blue spines jutting from its gaseous core; a pair of glowing yellow eyes and a jagged red mouth completed the look.

Aesthetics were far from the only difference. The Cloudy Sunrises had been communal and extraordinarily timid, yet this thing was forward and aggressive and, as far as Aqua could tell, operated on its own. But by far the most surprising aspect of it was its ability. If the Cloudy Sunrises had possessed any intrinsic power other than manipulating their vaporous form, Aqua had never observed it. This Heartless, however, was capable of suffusing itself into nearby material. It took over trees, turning dried branches into reaching hands and twisting bark into a parody of a face; it seeped into stone, the material darkening in color and seeming to rise under its own power. From her observations, Aqua eventually decided to name it the Possessor.

Though the Possessor appeared to take genuine pleasure out of manipulating objects, that was far from the only thing it possessed material for. At first, Aqua had wondered how such a small, solitary monster would compete with its fellows. Yet whenever other Heartless harangued it, it was quick to turn the environment itself against them. On one memorable occasion, it had possessed the headless statue of a horse that had been swallowed by darkness, transforming the stone steed into an engine of destruction that trampled over its lesser brethren. Aqua found herself admiring the creature’s contempt for its fellows—and also found herself alarmed at its versatility. In the Realm, where there was precious little to go around, its puppeteering was one thing. But if the Possessor or its kind ever made their way into the Realm of Light, then the ephemera at their disposal would be formidable indeed. What if it took over war machines?

She followed it for some days, always managing to keep out of sight—it did not appear especially perceptive or investigative. Eventually, that concern of hers was what prompted her to reveal itself. If it ever escaped into the Realm of Light, it could turn warriors’ weapons against themselves. Heartless on their own were already difficult for those who didn’t wield Keyblades; how terrible would it be if they could not defend themselves at all?

She waited until after it was finished possessing something on the off chance that it was weakened after using its ability; she had followed it to what seemed to be the remnants of a ruined courtyard. Crumbling, half-collapsed archstones stood sentinel over pebbled cobblestones, and a fountain— still somehow gushing a quiet trickle of water—stood in the center.

When the Possessor emerged from the fountain, she made her move. She bolted from behind the pillar, sending a spray of light magic its way. The Possessor hissed and bobbed sideways. It immediately vanished into the ground itself, and cobblestones darkened with shadow magic as the Possessor animated them to hurl at its opponent. Aqua cartwheeled out of the way, sending another rain of light at the spot the Possessor had melted into, but the stone shielded it from her attack. She cried out, warlike, and the Possessor’s shriek shook the stones in response.

And then all hell broke loose.

Perhaps they had been drawn by the kerfuffle or perhaps they had been stalking Aqua for a while, but a stampede of Heartless broke out of the gloom, making for her. Aqua cursed. She hadn’t counted on having to fight the Possessor and its kin at the same time!

She ducked under the slashing talons of a Wyvern, freeing its captive heart with a retaliatory slash, and vaulted over a creature she had unimaginatively named a Darkball. The Heartless snagged her ankle mid-leap with a shadowy tendril and smashed her down into the cobblestones. As Aqua’s world spun from the impact, two Air Soldiers swooped low only to be pelted out of the sky by more cobblestones. The Possessor’s scream rang out again and then a plume of earth shot out, burying the Darkball and freeing Aqua. As she rolled to her feet, her head clearing, the Keyblade Master marveled at the Heartless’s power. It seems it hates its fellows even more than it does me, she thought.

An invisible truce fell into place between her and the Possessor, and she responded with a powerful Firaga that smashed into a piratical baddie she had named the Anchor Raider. As more Heartless burst into the plaza, some of them—dust-manipulating Earth Cores—melted into the ground, chasing out the Possessor. As they cornered it, Aqua impulsively saved the very creature she had sought to attack, unleashing a powerful Waterga attack that snatched the Earth Cores with watery tendrils and squeezed them into nothingness. The Possessor shot her a look and then turned to the fountain.

Seeping into it, the Possessor’s darkness discolored the fountain—and then there was a crunching sound as the fountain rose from the earth and directed itself at the remaining Heartless. The splash of water quickly became a geyser of dark energy, cannoning the remaining Heartless away.

As the battlefield quieted, Aqua half expected the Possessor to turn the fountain’s might on her—but with a grinding noise, it returned it to its original position and then slowly seeped out, the shadows possessing the stone congealing into an inky blob of darkness. As the Possessor sulkily eyed her, Aqua kept her Keyblade levied at it for a moment and then lowered her weapon.

“Yeah,” she said, “I guess I deserve that mistrustful look. I did strike first.” She banished her Keyblade and the Heartless seemed slightly more at ease. What had she been thinking? Sure, the Possessor would be dangerous if let loose, but so would the likes of the Dark Hide or the Stealth Sneak. That still hadn’t stopped her from giving them a chance. And it not only seemed hostile to other Heartless, it had even saved her despite her turning her Keyblade on it!

I almost made a grave mistake.

“Here,” she said, proffering her hand. The creature retreated with a hiss, but on realizing she no longer meant it harm, it inched forward. It held near her outstretched hand with an air that reminded Aqua of a dog sniffing a new companion for the first time. She smiled encouragingly when it raised its yellow eyes to her.

And then, seemingly coming to a decision, it suddenly moved. Like the Cloudy Sunrises, it wound its way around her arm—but then Aqua gasped as its vapor suddenly suffused into her.

Immediately her body felt chill and trembling, the sensation starting in her arm where the Heartless had entered her but quickly dominating her entire body. Aqua fought to take a few tottering steps, each movement like fighting through molasses, each one harder than the next. She saw with alarm the telltale signs of the Possessor’s control—black-and-purple coloration—winding in spiraling patterns across her skin. As the patterns spread, so did the chill sensation, and before long, Aqua was completely incapable of controlling herself.

And then, suddenly, a second presence asserted itself in her head.

WARM. NEW. The presence reached out her hand, wiggling and flexing her fingers experimentally. The pattern of possession wound down her arm, disappearing under her fingerless gloves to re-emerge on her fingers themselves. The newcomer commanded her to move and spin. Her body’s movements were uncertain at first, but her new passenger was a swift learner. Before long, Aqua’s body was moving just as adroitly as she herself could maneuver it.

PLEASANT. NEW. PLAY. The thoughts came to her unbidden, pushed her way by the Possessor. Aqua had a sole breath to wonder play? before her body suddenly heeded the presence’s command and began racing off. Had she been in control of her faculties, she would have yelped; as was, she could only feel overwhelmed by the sudden rush of sensation. The Possessor led her on a merry chase; her body cartwheeled, skipped, and tumbled over the plaza, eventually collapsing from exhaustion, its lungs burning as it heaved for breath. From the Possessor riding along with her, Aqua could feel genuine enjoyment from the Heartless as it gloried in the sensations of playing in a flesh-and-blood body. Even the sense of being out of breath was novel to it.

Eventually, the creature bade her body to rise and make its way to the fountain. Peering over the rim, Aqua would have gasped if she could. Staring back at her from the water’s reflection was herself, but with spiraling black patterns slowly undulating across her arms and face like a living tattoo. Her sapphire hair had darkened to a nebulaic purple, and her eyes glowed the same yellow as the Possessor’s. The Heartless in her body smiled at seeing its new vessel, and then frowned with interest as it noticed something in its—her?—reflection. It reached down to the water with her shadow-stained fingers, touching the reflection of her breasts. Its touch disturbed the water with ripples, and it stepped back and looked down. Aqua’s own generous bosom stared back at them.